The usefulness of various chlorinated lower aliphatic hydrocarbons, particularly for the liquid and/or vapor phase degreasing of metals, is by now well known. Besides their excellent cleaning properties, these chlorinated solvents are well suited for industrial use owing to their lack of flammability and relatively low cost. The most widely used of these solvents are carbon tetrachloride, trichloroethylene, perchloroethylene and methyl chloroform (1,1,1 -trichloroethane). Of particular interest from this group is methyl chloroform, the excellent solvency and low toxicity of which make it particularly suitable for the industrial cleaning (degreasing) of metals.
A problem wide the commercialization of methyl chloroform has arisen, however, owing to its pronounced tendency to decompose in the presence of a number of metals, especially aluminum. Thus, while others of the chlorinated solvents, such as perchloroethylene, must be stabilized against decomposition induced by a wide variety of factors, the problem is nowhere near as marked as in the case of methyl chloroform, which, if exposed unprotected to aluminum, will be rendered useless within a matter of minutes.
Thus it will be apparent, and indeed research has shown, that while other chlorinated solvents may be stabilized through the use of small quantities of a wide variety of substances, the compounds capable of stabilizing methyl chloroform against metal-induced decomposition are quite limited in number and generally must be used in comparatively large amounts. Obviously, the requirements being strict and the selection limited, a number of problems have arisen in attempting to perfect a stabilizer system which will protect methyl chloroform and the metals being treated therewith against decomposition in both the liquid and vapor phases in the presence of a wide variety of contaminants. First, relatively large quantities being required, the stabilizers must be economically practical. Further, while the problems of liquid phase stabilization are often different from those of vapor phase stabilization and hence different stabilizers will be useful, the methyl chloroform may be used interchangeably for both liquid and vapor degreasing applications and therefore the components must be compatible over a wide range of temperatures.
While generalizations are indeed difficult with respect to the stabilization of methyl chloroform, it may be safely stated that many of the stabilizer systems used commercially and set forth in the patent literature describe and feature the use of nitroalkanes and epoxides. Although it is true that many stabilizer systems are "built" from this nitroalkane-epoxide base, the combination itself is not always completely effective for the stabilization of methyl chloroform and it is the selection of the remaining components of any system which determines its ultimate success or failure.